Help w a math question. I think it would be A right?

7. if the value of x varies directly with the value of y, and x = 3 when y = 21. what is the valu y, and x = 3 when y = 21. what is the value of x when y = 105?

15 there is a line that includes the point 0,10 and has a slope of 7/4. what is it’s equation in slope intercept form

Which of the following constants can be added to x2 - 3x to form a perfect square trinomial?